The present invention relates to a method for partially treating a water-repellent glass sheet to remove part of a water-repellent function of the glass sheet. The invention also relates to a water-repellent glass sheet with part of its water-repellent film removed.
In recent years, water-repellent glass sheets are widely used on vehicles so as to repel rain drops from fields of view of drivers of the vehicles to thereby ensure safety driving in a rainy weather.
Such glass sheets are known from, for example, Japanese Patent Laid-Open Publication Nos. HEI-4-130032 and HEI-4-305037. The glass sheet disclosed in Japanese Patent Laid-Open Publication No. HEI-4-130032 includes a glass substrate, a film of SiO2 (silicon dioxide) formed on the glass substrate, and a fluorine-based film such as that of fluorosilicon coated on the film of SiO2. The fluorine-based film provides a desired water-repellent function. In Japanese Patent Laid-Open Publication No. HEI-4-305037, the glass sheet is disclosed which comprises a glass substrate, a film of SiO2 formed on the glass substrate, and a fluorine-containing carbonaceous film formed on the film of SiO2. The fluorine-containing carbonaceous film provides a desired water-repellent function.
These glass sheets have prolonged lives because the water-repellent films formed thereon do not peel off easily.
Of vehicular glass sheets, a water-repellent pane of glass provided sidewardly of a vehicle has a lower portion connected to a lift mechanism called a window regulator for raising and lowering the pane of glass. More specifically, the water-repellent pane of glass is connected to holders of metal by means of resin or adhesive applied thereto. The holders are then bolted to arms of the lift mechanism. The holder can be readily adhered to a laminated glass pane or another glass pane free from a water-repellent function. However, a problem is encountered in connecting the holders to a water-repellent pane of glass by means of an adhesive. More specifically, it is impossible to achieve a required adhesive strength between the adhesive and the glass pane because the water-repellent film of the water-repellent pane of glass functions to repel the adhesive. As a consequence, the holders cannot be attached to the water-repellent glass pane. To overcome this problem, either abrasives (abrasive method) or masking tapes (masking tape method) have been conventionally used.
In the abrasive method, portions of the water-repellent film that are to be connected to the holders are scraped off mechanically by use of the abrasives containing small particles of silicon oxide or cerium oxide, thereby providing the water-repellent pane of glass having parts free of the water-repellent film. Such water-repellent-film-free parts of the glass pane can then be connected to the holders through an adhesive applied thereto.
In the masking tape method, portions of a pane of glass that are to be connected to the holders are masked by applying a masking tape thereto. A water-repellent film is then formed on the glass pane having the masked portions. Thereafter, the masking tape is peeled off from the glass pane, thereby providing the water-repellent glass pane with the portions free of the water-repellent film. Such water-repellent-film-free portions of the glass pane can then be connected to the holders through an adhesive applied thereto.
However, in the abrasive method, it is difficult and laborious to partially remove the water-repellent film by means of abrasives, thereby increasing the cost of processing of the water-repellent film.
Again, in the masking tape method, it is troublesome and laborious to apply masking tapes to the glass pane and to peel off the tapes from the glass pane. Further, it is quite difficult to achieve minute masking on the glass pane. Thus, the masking tape method is not effective for a curved pane of glass.
Reference is now made to FIG. 8 hereof schematically illustrating a conventional front glass pane or windshield. As in some conventional windshields, the illustrated windshield 101 includes wipers 102, 102 movable across the windshield to remove rain, and optical instruments such as a rain sensor 103 for detecting whether any rain drops are present on the windshield, or the amount of the rain drops on the windshield.
In FIG. 9, the windshield 101 with the rain sensor 103 is illustrated in enlarged-scale partial cross section taken along line 9xe2x80x949 of FIG. 8. The windshield 101 has a water-repellent film 104 formed on an external surface of the windshield 101. The water-repellent function of the film 104 becomes gradually degraded with the lapse of years. In correspondence with the degradation, the states of adherence of rain to the windshield 101 also change. It is quite tedious to make the relevant control follow those changes. In the light of the tedious adjustments thus required of the control to follow the changes, the front glass pane 101 may as well go without the water-repellent film 104.
To this end, one may propose to provide a small window-shaped water-repellent-film-free part 105 so that the rain sensor 103 can be mounted to the windshield 101 in opposed relation to the film-free part 105. This arrangement enables automatic wiping wherein the wipers 102, 102 are automatically operated in correspondence with the amount of rain present on the film-free or non-repellent part 105 of the windshield 101. It also becomes possible to urge, by signals, or phonetic or optical means, a driver to start the wipers.
Incidentally, for prolonging the life of the water-repellent film 104, it is desirable to provide a relatively thick ground film or undercoat of SiO2 interposed between the water-repellent film 104 and the front glass pane 101.
Now, the non-repellent part 105 may be formed in the water-repellent film 104 and the ground film laid thereunder by using either the abrasive method or the masking tape method. However, since the water-repellent film 104 is relatively thick, resulted edges 106 of the film 104 inevitably lie perpendicularly to a windshield surface on which the water-repellent film 104 is formed. Thus, it is liable to happen that an incident ray 107 originating from a source of light such as light of a car running on an opposite lane is reflected by the edges 106 to thereby cause mis-detection of the rain sensor 103. The abrasive method and the masking tape method are therefore not suited to form the window-shaped non-repellent part 105 in front of the sensor.
Reference is made next to FIG. 10 which schematically illustrates interrelations between a conventional door glass pane and a conventional door mirror. A driver, not shown but seated in a driver seat 111 with his hands held onto a steering wheel 112, looks into the door mirror 115 through the door glass pane 114 for rearward confirmation.
A front glass pane 116 has a water-repellent function because rain falls directly onto it. In contrast, the sideward door glass pane 114 normally comprises a non-water-repellent sheet of glass. It is, however, desirable that the door glass pane 114 has a water-repellent part 117, as illustrated, so that the driver can obtain a clear rear view of the mirror through the water-repellent part.
As can be readily appreciated, the water-repellent part 117 is surrounded by a non-water-repellent part 118 of the door glass pane 114. When the non-water-repellent part 118 is provided by means of the abrasive method or the masking tape method, an edge 119 of the water-repellent part 117 lies normal to a surface of the door glass pane 114. Then, it is likely that the edge 119, when shone with rays of light from a succeeding car or a passing-by car, or with roadside lights, undesirably serves as a reflecting surface and shines to thereby block the driver""s rear view. In this instance, the water-repellent part 117 loses its significance of being provided.
It is accordingly an object of the present invention to provide a method for removing part of a water-repellent film formed on a glass sheet, without using abrasives and/or masking tapes.
Another object of the present invention is to provide a water-repellent sheet of glass free from the foregoing optical inconveniences.
To attain the above objects, there is provided, in accordance with one aspect of the present invention, a method for partially treating a water-repellent glass sheet to remove part of a water-repellent function of the glass sheet, which method comprises the steps of: providing a glass sheet having a water-repellent film formed thereon; and irradiating a desired part of the water-repellent film with a stream of plasma jets to thereby eliminate the desired film part.
Since the plasma jet stream is limited in its radial expansion and narrower than a gas flame, it is possible to treat a desired portion of the water-repellent film precisely. The plasma jet irradiation may be effected by moving a plasma jet irradiation gun relative to and along a surface of the water-repellent film. Since such movement of the plasma jet irradiation gun can be achieved with no difficulty, the intended treatment can be accomplished readily even when the water-repellent glass sheet has a curved surface.
In a preferred form, the water-repellent glass sheet includes an SiO2-based undercoat interposed between a surface of the glass sheet and the water-repellent film. The desired-film-part elimination may be carried out such that the undercoat is left as it is.
Provision of the SiO2-based undercoat enables bonding of the water-repellent film with the water-repellent glass sheet with increased firmness. Further, with the undercoat remaining present at the repellent-film-eliminated part, optical problems as found in the conventional arrangement can be prevented.
Preferably, the plasma jet irradiating step is performed by using a plasma jet irradiation gun which is set to operate at a power output of the order of 0.5 kW, is positioned 5-15 mm distant from the glass sheet and is set to move at a velocity of 1-60 mm/sec parallel to a surface of the glass sheet in each pass of treatment.
When the distance between the plasma jet irradiation gun and the surface of the water-repellent glass sheet is less than 5 mm, stable plasma jet stream cannot be secured. Again, the distance of more than 15 mm is too long to provide a stable plasma jet stream. Thus, the distance is preferably set to fall in a range of 5 mm to 15 mm.
The term xe2x80x9cconversion velocityxe2x80x9d used herein represents a rate obtained when a velocity of movement of the plasma jet irradiation gun parallel to the surface of the water-repellent glass sheet is divided by the number of times the water-repellent glass sheet is treated with plasma jets. The conversion velocity is set to be 1 mm/sec or more, preferably 10 mm/sec or more, and more preferably 20 mm/sec or more while the conversion velocity is set to be 60 mm/sec or less, preferably 50 mm/sec or less, and more preferably 40 mm/sec or less. By using these parameters, a stable plasma jet stream is provided to thereby efficiently remove a desired part of the water-repellent film.
According to another aspect of the present invention, there is provided a water-repellent glass sheet produced by the partial treatment method described above. The glass sheet may be a curved one because it is treated by the plasma jets which achieve precise treatment.
According to a further aspect of the present invention, there is provided a water-repellent glass sheet which comprises an SiO2-based undercoat formed on a surface of said glass sheet; and a water-repellent film formed on the undercoat. The water-repellent film has non-water-repellent portions provided by nullifying a water-repellent function at portions thereof where a water-repellent function is not required, and a sloped border portion separating the non-water-repellent portions and remaining water-repellent portion. The sloped border portion has a gradient water-repellent function.
At the sloped border portion where the water-repellent function is gradient, the thickness of the water-repellent film decreases gradually from 10% to 0%. As a result, undesirable shining of the border portion and mis-operation of a rain sensor disposed inside a car, which are caused by rays of light of a passing-by car shining onto the border portion and the sensor, can be prevented.
It is desirable that the undercoat remains present at the non-water-repellent portions. With the undercoat kept present at those portions, no large stepped portion will be formed thereat, whereby optical problems due to light reflection, otherwise occurring at those portions, can be avoided.
The undercoat may be formed by a sol-gel process which enables film forming at a low-temperature atmosphere. This leads to increased productivity and hence reduction in the cost of production.